Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.30   4.407%   $61.9134   $61.91   $61.90   $61.90  
  Purchase #2 $21.38   10.297%   $23.5815   $23.58   $23.60   $23.60  
  Purchase #3 $50.49   9.602%   $55.338   $55.34   $55.35   $55.30  
  Purchase #4 $226.44   9.805%   $248.6424   $248.64   $248.65   $248.60  
  Purchase #5 $22.67   5.184%   $23.8452   $23.85   $23.85   $23.80  
  Purchase #6 $153.45   5.257%   $161.5169   $161.52   $161.50   $161.50  
  Purchase #7 $121.52   10.561%   $134.3537   $134.35   $134.35   $134.40  
  7 purchase totals = $655.25       $709.1911   $709.19   $709.20   $709.10